Field of the Invention
The present invention relates to technologies of controlling motors, and in particular, those used in image forming apparatuses.
Background
Electrophotographic image forming apparatuses such as laser printers use motors to actuate a variety of movable members. For example, such an apparatus rotates conveyance rollers to carry a sheet within the apparatus; the apparatus rotates a photoreceptor drum to allow its circumference surface to undergo steps of an image forming process, such as electrostatic charge, exposure, developing, transfer, and cleaning, in turn; the apparatus rotates a developing roller to allow its circumference surface to attract toner particles and then make them adhere onto a photoreceptor drum; the apparatus rotates an intermediate transfer belt to allow its surface to receive a toner image from a photoreceptor drum and then transfer it onto a sheet.
For recent image forming apparatuses, there has been developed a technology of separating from motors their driver circuits, esp. their controller circuits, more specifically pre-driver integrated circuits, and of integrating them with the controller circuits of the apparatuses. This technology prevents such a motor from overheating as follows.
Since separated from the motor, its controller circuit cannot detect an actual amount of rise in temperature of the motor, i.e., a difference in temperature between the motor and its surroundings. The controller circuit also cannot measure an amount of electric current of the motor if the circuit has no new sensor. The controller circuit thus, in order to prevent the motor from overheating with conventional configuration, estimates an amount of rise in temperature of the motor from the input value therefor. For example, a controller circuit disclosed in JP 2008-012850 estimates an amount of rise in temperature of a motor from the number of times that a duty ratio for pulse width modulation (PWM) control, i.e., a proportion of a pulse width to a period of pulse current or pulse voltage applied to the motor, exceeds a threshold value. Another controller circuit disclosed in JP 2003-079186 estimates an amount of heat generated by a motor from an amount of current of the motor. Either of these controller circuits, when having found a risk of overheating a motor from an estimated amount of temperature rise or heat generation of the motor, reduces rotation rates of the motor or enlarges time intervals of driving the motor. In addition, the controller circuit communicates and cooperates with the controller circuit of the apparatus to synchronize action of an object that the motor should drive with action of other movable members. The controller circuit thus, without overheating the motor, allows the apparatus to continue to process a job.
This technology, as discussed above, never forces to cut off power supply to a motor, even when having found a risk of overheating the motor, in contrast to overheat protection circuits embedded into general controller circuits. Accordingly, the motor is never subjected to any sudden braking force, and thus, any movable member that the motor should drive, such as a conveyance roller or a photoreceptor drum, is never forced to abruptly stop moving. The technology therefore prevents the overheat protection from jamming sheets and damaging surfaces of photoreceptor drums and the like.